Plasma confinement ring assemblies having reduced polymer deposition characteristics

ABSTRACT

Plasma confinement ring assemblies are provided that include confinement rings adapted to reach sufficiently high temperatures on plasma-exposed surfaces of the rings to avoid polymer deposition on those surfaces. The plasma confinement rings include thermal chokes adapted to localize heating at selected portions of the rings that include the plasma exposed surfaces. The thermal chokes reduce heat conduction from those portions to other portions of the rings, which causes selected portions of the rings to reach desired temperatures during plasma processing.

BACKGROUND

Plasma processing chambers can include an upper electrode and a lowerelectrode. The upper electrode typically faces a substrate supportadapted to support a semiconductor substrate during plasma processing.During the plasma processing, power is supplied to one or bothelectrodes to activate the process gas and produce the plasma to processthe substrate.

Plasma etching can be performed in plasma processing chambers to etchselected materials provided as layers on a semiconductor substrate. Theprocessing conditions are chosen so that the plasma etches desiredfeatures in selected portions of the layers.

SUMMARY

A preferred embodiment of a plasma confinement ring assembly for aplasma processing chamber comprises a plurality of plasma confinementrings. Each of the plasma confinement rings includes an inner portionhaving a plasma-exposed inner diametric surface, an outer portiondisposed radially outwardly from the inner portion, and at least onethermal choke. The thermal choke is adapted to reduce heat conductionfrom the inner portion to the outer portion when the inner diametricsurface is exposed to plasma in the plasma processing chamber. As aresult, the inner diametric surface reaches a sufficiently hightemperature to substantially prevent polymer deposition thereon.

Another preferred embodiment of a plasma confinement ring assembly for aplasma processing chamber comprises a mounting ring and a plurality ofplasma confinement rings adapted to be suspended below the mountingring. The plasma confinement rings comprise an upper plasma confinementring and a plurality of lower plasma confinement rings. The upper plasmaconfinement ring includes a top surface facing the mounting ring and aplasma-exposed bottom surface disposed radially inward from the secondplasma confinement rings. At least a portion of the top surface of theupper plasma confinement ring is opaque to IR radiation so as to enhanceheating of the upper plasma confinement ring. As a result, the bottomsurface reaches a sufficiently high temperature to substantially preventpolymer deposition thereon when the bottom surface is exposed to theplasma.

A preferred embodiment of a method of processing a semiconductorsubstrate in a plasma processing chamber comprises supplying a processgas into a plasma processing chamber comprising a plurality of plasmaconfinement rings, which each include a plasma-exposed surface; andproducing a plasma from the process gas and etching a semiconductorsubstrate in the plasma processing chamber. During the etching, theplasma-exposed surfaces of the plasma confinement rings reach asufficiently high temperature to substantially prevent polymerdeposition thereon.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 illustrates a portion of a preferred embodiment of a plasmaconfinement ring assembly.

FIG. 2 illustrates a top plan view of a portion of a preferredembodiment of a plasma confinement ring of the plasma confinement ringassembly, wherein the ring includes a thermal choke.

FIG. 3 is an enlarged partial top view of the plasma confinement ringshown in FIG. 2.

FIG. 4 illustrates a side view of another preferred embodiment of aplasma confinement ring of the plasma confinement ring assembly, whichhas a two-piece construction.

FIG. 5 illustrates a plasma processing chamber including a preferredembodiment of the plasma confinement ring assembly.

FIG. 6 depicts an embodiment of the plasma confinement ring assemblywithout thermal chokes that was used in Examples 1 and 2.

FIG. 7 depicts an embodiment of the plasma confinement ring assemblyincluding thermal chokes that was used in Example 3.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Parallel-plate plasma processing chambers, such as capacitively-coupledchambers, include an upper electrode, such as a showerhead electrode,and a lower electrode. The upper electrode typically faces asemiconductor substrate to be processed. During the plasma processing,power is supplied to one or both electrodes to activate the process gasand produce the plasma to process the substrate.

Interior surfaces of such plasma processing chambers can be poweredsurfaces (e.g., “RF hot surfaces”), grounded surfaces, or floatingsurfaces (comprised of insulating materials). Different energy issupplied to, or impinges, on these different types of surfaces duringplasma processing. Particularly, heating of a chamber part in aparallel-plate plasma processing chamber depends upon the ion energy andthe ion flux supplied to the part's exposed surfaces, and on theinfrared (IR) energy absorption characteristics of the part. Grounded(return path) surfaces and powered surfaces receive significant ionenergy from plasma, which causes these surfaces to be heated more thanfloating parts or surfaces, and also to reach significantly differenttemperatures.

Highly-polymerizing process gas chemistries, such as process gasescontaining fluorocarbons, hydrofluorocarbons, or precursors of suchgases, can be used to etch dielectric materials, such as silicon oxide.During such plasma etch processes, polymer tends to deposit on someinternal surfaces of the plasma processing chamber. The polymer depositsare undesirable because they can flake off of the surfaces andcontaminate processed substrates (e.g., processed wafers), as well asthe chamber. However, as device features continue to shrink, it becomesincreasingly desirable to maintain plasma-exposed chamber surfaces cleanfrom wafer-to-wafer to achieve repeatable process results. Accordingly,it is desirable to reduce, and preferably to avoid, such polymerdeposits on internal surfaces of chamber parts.

Generally, polymer deposits are more likely to form on coolerplasma-exposed surfaces of the plasma processing chamber during plasmaprocessing operations. Floating surfaces tend to be cooler surfaces andconsequently are generally more prone to develop polymer buildup on themas compared to powered or grounded surfaces. The temperature increase,ΔT, of a plasma-exposed part or surface during plasma processing dependson the amount of heat, Q, added to the part or surface, and the mass, m,and the specific heat, c, of the part; according to the followingrelationship: Q=mcΔT. Accordingly, for a given amount of heat added to apart, increasing the part mass decreases the increase in temperature ofthe part. Consequently, a part having a high mass may not reach asufficiently high temperature during plasma processing to avoid polymerdeposition on plasma exposed surfaces of the part. Increasing the heatcapacity of a part also decreases the temperature reached by the partfor a given amount of heat added to the part.

In addition, during plasma processing, heat can be transferred to and/orfrom a part to other chamber surfaces by thermal conduction (when thepart is in physical contact with another surface), radiation (whenelectromagnetic waves carry heat to and/or from the part) and convection(when heat is carried by a moving fluid in the chamber). Convective heatlosses from parts increase with increasing chamber pressure.

The problem of polymer deposition on plasma-exposed surfaces of someparts in plasma processing chambers can be addressed by actively heatingthe part(s). For example, chamber walls can be heated to keep theirplasma-exposed interior surface(s) at a sufficiently high temperature toavoid polymer deposition on the surface(s). Active temperature controlof showerhead electrode assemblies and electrostatic chucks can also beused. However, as such surfaces are powered or grounded and consequentlysubject to high ion energy, polymer deposition on these surfaces is lesslikely to occur than on a floating surface even without active heatingof the surfaces.

Alternatively, the polymer deposition problem can be addressed byremoving as-formed polymer deposits from surfaces. For example, polymerdeposits can be removed by employing aggressive plasma chemistries.Alternatively, the plasma chamber can be opened and a wet cleaningtechnique can be used to remove polymer deposits from chamber surfaces.However, such cleaning techniques reduce process throughput.

In order to achieve desirable process efficiency and etch uniformity,plasma can be confined within a plasma confinement zone defined betweenthe upper and lower electrodes of a parallel-plate plasma processingchamber. Plasma confinement ring assemblies can be used to provide suchplasma confinement. Exemplary plasma confinement ring assemblies aredisclosed in commonly-owned U.S. Pat. Nos. 5,534,751; 5,998,932;6,019,060; 6,178,919 and 6,527,911, each of which is incorporated hereinby reference in its entirety. As described in U.S. Pat. No. 5,534,751, aplasma confinement ring assembly can include a plurality of plasmaconfinement rings, which are arranged in a stack to define a pluralityof gas passages extending radially through the rings from an inner to anouter surface. Charged particles in the plasma are neutralized as theparticles pass through the passages, thereby minimizing the tendency fora discharge outside the plasma confinement zone (i.e., “unconfinement”of the plasma).

As also described in U.S. Pat. No. 5,534,751, plasma confinement ringassemblies may confine polymer deposition during plasma etch processesto only the plasma confinement rings themselves. However, it isdesirable to avoid such polymer deposition on the confinement rings inorder to avoid potential chamber and substrate contamination problems,as well as to avoid additional chamber cleaning steps to removeas-formed polymer deposits from the plasma confinement rings.

In light of the above-described polymer deposition problem, it has beendetermined that plasma confinement ring assemblies can be provided thatinclude confinement rings adapted to reach sufficiently hightemperatures on plasma-exposed surfaces of the rings to avoid polymerdeposition on those surfaces, without employing active heating of thesurfaces. More particularly, the plasma confinement rings are adapted tolocalize heating at selected portions of the rings that include theplasma exposed surfaces. Heating is localized at these selected portionsby providing one or more thermal chokes in each of the rings at selectedlocations to thereby reduce heat conduction from those portions to otherportions of the rings that otherwise act as heat sinks in confinementrings without the thermal chokes.

FIG. 1 depicts a preferred embodiment of a plasma confinement ringassembly 10. The plasma confinement ring assembly 10 comprises, in aconcentric arrangement, a mounting ring 12 and plasma confinement rings14,16, 18 and 20 suspended from the mounting ring 12. The mounting ring12 and plasma confinement rings 14,16, 18 and 20 are vertically-movableto provide adjustment. The number of plasma confinement rings of theassembly is not limited to four rings, as shown; alternatively, therecan be less than four rings, e.g., three rings, or more than four rings,e.g., five, six or more rings.

The mounting ring 12 and the plasma confinement rings 14,16, 18 and 20are floating parts comprised of a suitable electrically insulatingmaterial (dielectric). The insulating material can be, for example,quartz, fused silica, silicon nitride, alumina, or a plastic material.High-purity quartz is a preferred material for use in etch processes fordielectric materials. In the embodiment, the mounting ring 12 and eachof the plasma confinement rings 14,16,18 and 20 are of a single piece ofthe insulating material.

As shown in FIG. 1, the plasma confinement rings 14,16, 18 and 20 areconnected to the mounting ring 12 by a hanger 22 configured to extendthrough holes 24 in each of the plasma confinement rings 14, 16, 18 and20. An insert 26 is preferably provided in each hole 24 to preventdirect contact between the hanger 22 and the plasma confinement rings14,16, 18 and 20. A spring 28 is preferably provided on an inner shaft30 of the hanger 22 to resiliently bias the hanger 22 with respect to afitting 32 on the hanger 22.

For etching round semiconductor substrates, such as wafers, the plasmaconfinement rings 14,16,18 and 20 include an inner diametric surface 34,36, 38 and 40, respectively, and an outer diametric surface 42, 44, 46and 48, respectively. The inner diametric surfaces 34, 36, 38 and 40 areplasma-exposed surfaces. As shown in FIG. 1, the uppermost plasmaconfinement ring 14 has a greater width in the radial direction than theplasma confinement rings 16,18 and 20. As also shown, the innerdiametric surfaces 36, 38 and 40 of the respective plasma confinementrings 16,18 and 20 are preferably vertically aligned.

The inner diametric surface 34 of the plasma confinement ring 14 ispreferably vertically aligned with the inner diametric surface 50 of themounting ring 12. By this arrangement, the plasma confinement ring 14overlies the bottom surface 52 of the mounting ring 12. It has beendetermined that due to the relatively large thermal mass of the mountingring 12, without the plasma confinement ring 14, the bottom surface 52of the mounting ring 12 does not reach a sufficiently high temperatureto prevent polymer deposition on the bottom surface 52 during plasmaprocessing. By incorporating the plasma confinement ring 14 separatedfrom the bottom surface 52, the bottom surface 52 is protected fromexposure to plasma and polymer deposition on the bottom surface 52 ispreferably minimized.

In the embodiment, the plasma confinement rings 14, 16,18 and 20 includethermal chokes 54, 56, 58 and 60, respectively. Heat is supplied to theplasma confinement rings 14,16,18 and 20 by plasma and other heatingeffects during plasma etching processes. The thermal chokes 54, 56, 58and 60 reduce heat conduction in the radial outward direction from thelocations of the thermal chokes 54, 56, 58 and 60, to thereby enhanceheating of the inner portion of the respective plasma confinement rings14, 16,18 and 20 defined between the thermal chokes 54, 56, 58 and 60and the inner diametric surfaces 34, 36, 38 and 40, respectively.Consequently, each of the inner diametric surfaces 34, 36, 38 and 40preferably reaches a sufficiently high temperature to substantiallyprevent polymer deposition on these surfaces during plasma processing.

FIGS. 2 and 3 depict a portion of a preferred embodiment of a plasmaconfinement ring 120 including a thermal choke 160. In the embodiment,the mounting ring and/or one or more of the other plasma confinementrings of the plasma confinement ring assembly can also include a thermalchoke configured as shown in FIGS. 2 and 3.

The illustrated thermal choke 160 comprises a plurality of inner slots161 arranged in a discontinuous first circular pattern, and a pluralityof outer slots 163 spaced outwardly from the inner slots and arranged ina concentric discontinuous second circular pattern. Adjacent inner slots161 are separated by inner regions 165, and adjacent outer slots 163 areseparated by outer regions 167. As shown in FIG. 2, the inner regions165 and outer regions 167 are offset from each other around the plasmaconfinement ring 120. The inner slots 161 and the outer slots 163preferably extend completely through the thickness of the plasmaconfinement ring 120. This construction and placement of the thermalchoke 160 reduces radial heat transfer to the outer portion 169 of theplasma confinement ring 120, such that the inner diametric surface 140reaches a sufficiently high temperature to substantially prevent polymerdeposition on this surface during plasma processing.

The inner slots 161 and outer slots 163 preferably have a width of fromabout 0.005 inch to about 0.020 inch. In a preferred embodiment, theinner slots 161 and 163 are formed by a laser ablation technique.

In another preferred embodiment, one or more of the plasma confinementrings of the plasma confinement ring assembly 10 has a multi-piececonstruction. For example, the embodiment of the plasma confinement ring220 shown in FIG. 4 has a two-piece construction and comprises an innerring portion 221 and an outer ring portion 223. The inner ring portion221 includes a plasma-exposed inner diametric surface 240. The innerring portion 221 and the outer portion 223 are preferably comprised ofthe same insulating material.

In the plasma confinement ring 220, the inner ring portion 221 and outerring portion 223 are configured to minimize contact between surfaces ofthe inner ring portion 221 and the outer ring portion 223 at the region227 (which contact occurs due to gravity). At least one gap is definedbetween opposed surfaces of the inner ring portion 221 and outer ringportion 223. In the embodiment, the gaps 225 act as thermal chokes. Bythis construction of the plasma confinement ring 220, heat conductionfrom the inner ring portion 221 to the outer ring portion 223 occursonly at the region 227 where there is surface contact when the innerdiametric surface 240 of inner ring portion 221 is exposed to plasma.Consequently, the inner diametric surface 240 can reach a sufficientlyhigh temperature to substantially prevent polymer deposition on thesurface.

In a preferred embodiment, at least one surface of one or more of theplasma confinement rings of the plasma confinement ring assembly can beroughened and/or coated with a material that is opaque to IR (infrared)radiation and can block transmission of the IR radiation. In theembodiment, IR radiation incident on the confinement ring is transmittedthrough the body of the confinement ring, but is blocked by theroughened and/or coated surface. For example, the confinement ring canbe comprised of quartz, or another IR transparent insulting material. Byblocking the IR radiation, heating of a selected portion of theconfinement ring partially defined by the roughened and/or coatedsurface is enhanced.

Selected surfaces of the plasma confinement rings can be roughened by asuitable technique, such as shot peening or by machining the surfaceusing a diamond tool that produces a pitted surface. The surfaces can becoated with a suitable IR opaque material. Surfaces that are not exposedto plasma can be coated with alumina.

For example, as shown in FIG. 1, the upper surface 62 of the plasmaconfinement ring 14 can be roughened and/or coated with an IR opaquematerial in the region between the inner diametric surface 34 and thethermal choke 54. Consequently, IR radiation incident on the lowersurface 64 and/or inner diametric surface 34 of the plasma confinementring 14 is blocked by the roughened and/or coated upper surface 62,which thereby enhances heating of the portion of the plasma confinementring 14 between the inner diametric surface 34 and the thermal choke 54.As the surface 64 is not directly exposed to plasma, the IR opaquematerial can be of a material, such as alumina, that is not preferredfor use on plasma-confining surfaces.

In another preferred embodiment, selected surfaces that define the slotsformed in the plasma confinement rings can be roughened and/or coatedwith a material that is opaque to IR radiation. For example, in theembodiment of the plasma confinement ring 120 shown in FIGS. 2 and 3, atleast one of the surfaces 169 and 171 can be roughened and/or coatedwith an IR opaque material to block transmission of IR radiation toaffect further heating of the inner diametric surface 140.

FIG. 5 depicts an exemplary embodiment of a capacitively-coupled plasmaprocessing chamber 300 in which the plasma confinement ring assembly 10is mounted. The plasma processing chamber 300 includes an upperelectrode 302 having a bottom surface 304. In the embodiment, the bottomsurface 304 includes a step 306 adapted to control a localized densityof the plasma formed adjacent the exposed surface of the upper electrode302, as described in U.S. Pat. No. 6,391,787, which is incorporatedherein by reference in its entirety. In the embodiment, the upperelectrode 302 is a showerhead electrode including gas passages 308arranged for distributing process gas into the plasma processing chamber300. The upper electrode 302 can be comprised of silicon (e.g., singlecrystal silicon or polycrystalline silicon) or silicon carbide.

In the embodiment, the upper electrode 302 is a single-piece electrode(e.g., for 200 mm wafer processing). The upper electrode 302 ispreferably mounted (e.g., elastomer bonded) to a backing member 310 of asuitable material, such as graphite or silicon carbide. The backingmember includes gas passages 312 in fluid communication withcorresponding gas passages 308 in the upper electrode 302.

In another embodiment, the upper electrode can have a two-piececonstruction (e.g., for 300 mm wafer processing) and include asingle-piece inner electrode member and an outer electrode membersurrounding the inner electrode member, such as described incommonly-owned U.S. patent application Ser. No. 10/743,062, which isincorporated herein by reference in its entirety. In the embodiment, thebacking member preferably includes a backing plate co-extensive with theinner electrode member and a backing ring co-extensive with the outerelectrode member, as described in U.S. patent application Ser. No.10/743,062.

In the embodiment of the plasma processing chamber 300 shown in FIG. 5,a thermal control plate 314 is preferably provided on the backing member310. The thermal control plate 314 preferably includes one or moreheaters adapted to control the temperature of the upper electrode 302,as described in U.S. patent application Ser. No. 10/743,062.

The plasma processing chamber 300 includes a gas source (not shown) forsupplying process gas to the upper electrode 302. The process gas isdistributed in the chamber by the gas passages 308 in the upperelectrode 302. The upper electrode 302 can be powered by an RF powersource 316 via a matching network. In another embodiment, the upperelectrode 302 can be electrically grounded to provide a return path forpower supplied by a bottom electrode of the substrate support 320 of theplasma processing chamber 300.

In the embodiment, process gas is supplied into the plasma processingchamber 300 at the plasma generation region in the space between theupper electrode 302 and a semiconductor substrate 322, e.g., asemiconductor wafer, supported on a substrate support 320. The substratesupport 320 preferably includes an electrostatic chuck 324 that securesthe semiconductor substrate 322 on the substrate support by anelectrostatic clamping force. The electrostatic chuck 324 acts as abottom electrode and is preferably biased by at least one of the RFpower sources 326, 327 (typically via a matching network).

During plasma processing of the semiconductor substrate 322, the plasmaconfinement ring assembly 10 confines plasma in a plasma confinementzone between the upper electrode 302 and the semiconductor substrate322. Edge rings 326, 328 are preferably arranged in surroundingrelationship to the semiconductor substrate 322 to focus the plasma soas to improve etch uniformity.

A vacuum pump (not shown) is adapted to maintain a desired vacuumpressure inside the plasma processing chamber 300.

An exemplary parallel-plate plasma reactor that can be used is adual-frequency plasma etch reactor (see, e.g., commonly-owned U.S. Pat.No. 6,090,304, which is hereby incorporated by reference in itsentirety). In such reactors, etching gas can be supplied to a showerheadelectrode from a gas supply and plasma can be generated in the reactorby supplying RF energy at different frequencies from two RF sources tothe showerhead electrode and/or a bottom electrode. Alternatively, theshowerhead electrode can be electrically grounded and RF energy at twodifferent frequencies can be supplied to the bottom electrode.

EXAMPLE 1

In Example 1, a plasma confinement ring assembly 400 as shown in FIG. 6was used in a parallel-plate, capacitively-coupled plasma processingchamber. As shown, the plasma confinement ring assembly 400 generallyhas the same construction as the assembly 10 shown in FIG. 1; however,the plasma confinement rings 414, 416, 418 and 420 do not includethermal chokes. The plasma confinement rings were of quartz.

In Example 1, the following dielectric etch process conditions were usedto process 85 wafers: 45 mT chamber pressure/1100 W power at a frequencyof 2 MHz applied to bottom electrode/800 W power at a frequency of 60MHz applied to bottom electrode/300 sccm argon/15 sccm C₄F₈/10 sccmO₂/upper electrode temperature of 140°/bottom electrode temperature of20° C. An oxygen cleaning step was performed after etching each waferusing the following process conditions: 500 mT chamber pressure/200 Wpower at a frequency of 27 MHz applied to bottom electrode/300 W powerat a frequency of 60 MHz applied to bottom electrode/2000 sccm O₂/40seconds.

As shown in FIG. 6, temperatures were measured using thermocouplesattached at location A on the bottom surface 452 of the mounting ring412, location B on the top surface of the confinement ring 414, locationC at the top surface of the confinement ring 416, and location D at thetop surface of the confinement ring 420.

The following temperatures were measured at these locations during theplasma processing: location A—about 66° C/location B—about 110° C. toabout 116° C./location C—about 82° C./location D—about 82° C. to about104° C. Following etching of the wafers, the plasma processing chamberwas opened and the confinement ring assembly 400 was visibly examinedfor the presence of polymer deposition. No polymer deposition wasobserved on the plasma confinement ring 414. However, polymer depositionwas observed on the plasma-exposed, inner diametric surfaces 436,438 and440 of the plasma confinement rings 416, 418 and 420, indicating thatthese surfaces did not reach a sufficiently high temperature to preventpolymer deposition.

EXAMPLE 2

Example 2 used the plasma confinement ring assembly 400 shown in FIG. 6in a parallel-plate, capacitively-coupled plasma processing chamber toetch 100 wafers using the following dielectric etch process conditions:45 mT chamber pressure/1100 W power at a frequency of 2 MHz applied tobottom electrode/800 W power at a frequency of 60 MHz applied to bottomelectrode/300 sccm argon/28 sccm C₄F₈/13 sccm O₂/upper electrodetemperature of 140° C./bottom electrode temperature of 20° C. An oxygencleaning step was performed after etching each wafer using the followingprocess conditions: 500 mT chamber pressure/250 W power at a frequencyof 27 MHz applied to bottom electrode/125 W power at a frequency of 60MHz applied to bottom electrode/2000 sccm O₂/40 seconds.

Following etching of the wafers, the plasma processing chamber wasopened and the confinement ring assembly 400 was visibly examined forthe presence of polymer deposition. No polymer deposition was observedon the plasma confinement ring 414. However, polymer deposition wasobserved on the plasma-exposed, inner diametric surfaces 436, 438 and440 of the plasma confinement rings 416,418 and 420, indicating thatthese surfaces did not reach a sufficiently high temperature to preventpolymer deposition.

EXAMPLE 3

In Example 3, a plasma confinement ring assembly 500 as shown in FIG. 7was used in a parallel-plate, capacitively-coupled plasma processingchamber. As shown, the plasma confinement ring assembly 500 has the sameconstruction as the assembly 10 shown in FIG. 1, and includes thermalchokes 554, 556, 558 and 560 on the respective plasma confinement rings514, 516, 518 and 520. The thermal chokes 554, 556, 558 and 560 wereslots formed in a concentric, discontinuous circular arrangement, suchas shown in FIG. 2. The slots had a width of from about 0.010 inch toabout 0.015 inch and extended through the thickness of the plasmaconfinement rings 514, 516, 518 and 520.

In Example 3, the same etch process conditions that were used in Example2 were used to process 100 wafers.

As shown in FIG. 7, temperatures were measured using thermocouplesattached at location A on the bottom surface 552 of the mounting ring512; location B on the top surface of the confinement ring 514, inwardlyfrom the thermal choke 554; location C at the top surface of theconfinement ring 514, outwardly from the thermal choke 554; location Dat the top surface of the confinement ring 516, inwardly of the thermalchoke 556; and location E at the top surface of the confinement ring516, outwardly from the thermal choke 556. The following temperatureswere measured at these locations: location A—about 71° C. to about 77°C./location B—about 127° C. to about 132° C./location C—about 71° C. toabout 77° C./location D—about 116° C. to about 143° C./location E—about77° C. to about 82° C.

Following etching of the wafers, the plasma processing chamber wasopened and the confinement ring assembly 500 was visibly examined forthe presence of polymer deposition. No polymer deposition was observedon the plasma confinement ring 514 or on the plasma-exposed, innerdiametric surfaces 536, 538 and 540 of the plasma confinement rings 516,518 and 520, indicating that these surfaces reached a sufficiently hightemperature to prevent polymer deposition.

Referring to FIG. 1, the above-described test results demonstrate thatby incorporating the uppermost extended plasma confinement ring 14 inthe plasma confinement ring assembly, polymer deposition on the thickmounting ring 12 can preferably be prevented. In addition, by providingone or more thermal chokes in the plasma confinement rings 14, 16, 18and 20, polymer deposition on plasma exposed surfaces of the rings canpreferably be prevented.

The foregoing has described the principles, preferred embodiments andmodes of operation of the present invention. However, the inventionshould not be construed as being limited to the particular embodimentsdiscussed. Thus, the above-described embodiments should be regarded asillustrative rather than restrictive, and it should be appreciated thatvariations may be made in those embodiments by workers skilled in theart without departing from the scope of the present invention as definedby the following claims.

1. A plasma confinement ring assembly for a plasma processing chamber,comprising a plurality of vertically-stacked plasma confinement ringsconfining and surrounding a plasma space above a substrate support onwhich a semiconductor substrate is supported in the chamber, each of theplasma rings including an inner portion having a plasma-exposed innerdiametric surface, an outer portion disposed radially outwardly from theinner portion, and at least one thermal choke adapted to reduce heatconduction from the inner portion to the outer portion when the innerdiametric surface is exposed to plasma in the plasma processing chamber,such that the inner diametric surface reaches a sufficiently hightemperature to substantially prevent polymer deposition thereon, whereinthe at least one thermal choke comprises a plurality ofcircumferentially-extending slots which extend completely through thethickness of the plasma confinement ring, and each plasma confinementring comprises through holes which are spaced radially outward from theslots.
 2. The plasma confinement ring assembly of claim 1, wherein oneor more of the plasma confinement rings has a one-piece construction. 3.The plasma confinement ring assembly of claim 1, wherein the innerportion of one or more of the plasma confinement rings has at least onesurface that is roughened and/or coated with a material that blocks IRradiation incident on at least one other surface of the plasmaconfinement ring to thereby enhance heating of the inner portion of theone or more plasma confinement rings.
 4. The plasma confinement ringassembly of claim 1, wherein at least one of the slots of one or more ofthe plasma confinement rings is partially defined by a surface that isroughened and/or coated with a material that blocks IR radiationincident on at least one other surface of the one or more plasmaconfinement rings to thereby enhance heating of the inner portion of theone or more plasma confinement rings.
 5. The plasma confinement ringassembly of claim 1, wherein the at least one thermal choke of each ofthe plasma confinement rings comprises a plurality ofcircumferentially-extending first slots which extend around adiscontinuous first circle and a plurality ofcircumferentially-extending second slots which extend around aconcentric discontinuous second circle surrounding the first circle andare circumferentially offset from the first slots.
 6. The plasmaconfinement ring assembly of claim 1, wherein the slots have a width offrom about 0.005 inch to 0.020 inch.
 7. The plasma confinement ringassembly of claim 1, further comprising: a mounting ring; and theplurality of plasma confinement rings being suspended below the mountingring.
 8. A plasma processing apparatus, comprising: an upper electrode;a substrate support including a lower electrode; and a plasmaconfinement ring assembly according to claim 1 arranged to enhanceconfinement of a plasma in a space between the upper electrode and thesubstrate support.
 9. A method of processing a semiconductor substratein a plasma processing chamber, comprising: supplying process gas into aplasma processing chamber comprising a plasma confinement ring assemblyaccording to claim 1; and producing a plasma from the process gas andetching a semiconductor substrate in the plasma processing chamber;during the etching, the plasma-exposed inner diametric surface of eachof the plasma confinement rings reaches a sufficiently high temperatureto substantially prevent polymer deposition thereon.
 10. The method ofclaim 9, wherein the semiconductor substrate comprises a dielectricmaterial which is etched by the plasma, and the process gas contains atleast one constituent selected from the group consisting offluorocarbons, hydrofluorocarbons, fluorocarbon precursors andhydrofluorocarbon precursors.
 11. The method of claim 9, wherein theplasma processing chamber comprises a grounded upper electrode, and alower electrode to which power is applied at two different frequencies.12. The method of claim 11, wherein the upper electrode is a showerheadelectrode.
 13. The method of claim 9, wherein the plasma confinementrings each include a plurality of thermal chokes.
 14. The method ofclaim 13, wherein the thermal chokes are circumferentially-extendingslots.
 15. The method of claim 13, wherein one or more of the plasmaconfinement rings has at least one surface that is roughened and/orcoated with a material that blocks IR radiation.
 16. A plasmaconfinement ring for a plasma confinement ring assembly for a plasmaprocessing chamber wherein the plasma confinement ring assembly includesa plurality of vertically-stacked plasma confinement rings confining andsurrounding a plasma space above a substrate support on which asemiconductor substrate is supported in the chamber, the plasmaconfinement ring comprising: an inner portion having an inner diametricsurface adapted to be exposed to plasma in the plasma processingchamber; an outer portion disposed radially outwardly from the innerportion; at least one thermal choke comprising a plurality ofcircumferentially-extending slots extending completely through thethickness of the plasma confinement ring, the at least one thermal chokebeing adapted to reduce heat conduction from the inner portion to theouter portion when the inner diametric surface is exposed to plasma inthe plasma processing chamber, such that the inner diametric surfacereaches a sufficiently high temperature to substantially prevent polymerdeposition thereon; and through holes spaced radially outward from theslots.
 17. The plasma confinement ring of claim 16, which has aone-piece construction.
 18. The plasma confinement ring of claim 16,wherein the inner portion has at least one surface that is roughenedand/or coated with a material that blocks IR radiation incident on atleast one other surface of the plasma confinement ring to therebyenhance heating of the plasma confinement ring.
 19. The plasmaconfinement ring of claim 16, wherein the thermal choke comprises aplurality of circumferentially-extending first slots which extend arounda discontinuous first circle and a plurality ofcircumferentially-extending second slots which extend around aconcentric discontinuous second circle surrounding the first circle andare circumferentially offset from the first slots.
 20. The plasmaconfinement ring of claim 19, wherein the first and second slots eachextend completely through the thickness of the plasma confinement ring.